The purpose of this study is to investigate the possible efficacy and safety of new compounds applied to the treatment of certain disorders of movement, and to employ drugs as tools to analyze the physiological and pharmacological mechanisms mediating various motor deficits. The major conclusions deriving from observations over the last year are: (1) deprenyl has no significant therapeutic action in Parkinson's disease; paradoxically, for an inhibitor of monoamine oxidase, this induces a reduction in the plasma concentration of norepinephrine and epinephrine, without altering dopamine; (2) bromocriptine elicits a normal reduction of dopamine receptors in the anterior pituitary; (3) the erythromelalgia, produced as an adverse reaction to bromocriptine, is associated with mononuclear infiltration of the wall of dermal blood vessels; (4) the reduction of tetrahydrobiopterin in the cerebrospinal fluid, previously described in patients with Parkinson's disease, has also been recorded in other neurological diseases such as the Shy-Drager syndrome; (5) in twelve monozygotic twin pairs, one twin had Parkinson's disease without any evidence of neuropathology in the other twin. This finding implies an important role for an environmental factor in the etiology of this disorder.